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A.
Watershed Features
1. Stream Modifications Alterations to the shape, size, and vegetation along streams has occurred on many streams within the Darby Watershed in the past 200 years. The most prevalent modification that has occurred on streams is channelization and woody vegetation removal. Much of the stream channelization occurred between 70 and 80 years ago. In general, tributary streams in the central portion of the watershed have the most modification. Figure 82 displays the most prevalent stream modifications by type for the entire watershed. It is important to note that over 40% of all streams had no evident modification.
The straightening and/or deepening of streams through channelization is the most common stream modification in the watershed. The combination of both channelizing and removing woody vegetation along streambanks occurs on over 24 percent of streams in the watershed. Approximately 50 stream miles have been hydromodified, or
tiled in the past 20-30 years. The
streams database upon which this research was conducted displayed all open
channels, but was completed in the 1970s and 1980s.
Therefore any open channel that was no longer evident from aerial
photography or on the ground was determined to be tiled.
An example of hydromodification from development would be in Nearly 11 percent of the 24 percent of streams both channelized and lacking woody vegetation are under county maintenance. The following series of Figures 83-86 further define stream modifications by ranking the counties by the percent of modified stream miles within the Darby Watershed. Figures 81-84 do not include county maintained ditches.
A considerable amount of stream modification has occurred in most of the watershed particularly in the western counties. More detailed data will be utilized for stream segments not meeting water quality standards in each subwatershed plan.
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